\hbar new letter

Question

I would want to know in which package the symbol \hbar is defined. In fact I ask this because I need to create a letter like \hbar but with 'k' instead of 'h'.

Answer 1

\hbar is defined in the LaTeX kernel:

\newcommand{\hbar}{\mathchar'26\mkern-9mu h}

So

\newcommand{\kbar}{\mathchar'26\mkern-9mu k}

should do what you want (although it might need some customization if other fonts are used).